(1) Field of the Invention
The present invention relates generally to navigation, and more particularly to a method of navigating using waypoints.
(2) Description of the Prior Art
Waypoint navigation provides a means of directing a vehicle along a pre-planned path. A waypoint is a single point in a coordinate system. Usually, waypoints use earth coordinates of latitude and longitude degrees. Optionally, a depth or elevation may also be specified. Other coordinate systems may be used when appropriate to the mission or vehicle.
Typically, a starting and ending point are specified along with one or more intermediate waypoints. The vehicle proceeds from the starting point to the first intermediate waypoint. When the vehicle reaches a waypoint, it then changes course and proceeds to the next waypoint in sequence. This continues until the final waypoint has been reached. While such "point-to-point" waypoint navigation is sufficient in many situations, there are several instances where a more controlled method of navigation is required. This is particularly important where an autonomous (unmanned) vehicle is being employed. Since there are control errors in any real vehicle, it is unlikely that the vehicle will exactly cross any specified waypoint. Instead, there is an undesirable tendency for the vehicle to pass close by the waypoint, and then once past the waypoint, turn around and approach the waypoint from the opposite direction. To avoid this, it is necessary to devise a test or tolerance condition to determine when the waypoint has been reached so that the vehicle can proceed on to the next waypoint. In addition, if the waypoint is marked by a physical object such as a buoy, the vehicle may hit the object if it is being directed to the waypoint. A simple way to avoid this situation is to set the waypoint at some distance away from the actual marker. However, if a previous condition has forced the vehicle off course, then the vehicle may approach the modified waypoint on a path that still contacts the marker.